The present invention relates to a process for the production of an optoelectronic device, in particular a photovoltaic (PV) module or a light emitting diode (LED) device.
A popular substrate for the manufacture of optoelectronic devices (for example photovoltaic modules or light emitting diode devices) is glass coated with a conductive coating. Various conductive coatings are known, including those based on conductive metal oxides. Of these, important conductive metal oxides include indium tin oxide and tin oxide doped with e.g. fluorine.
However, one of the problems which has been identified in the use of various coated substrates in optoelectronic devices is that occasionally spikes of conductive material occur on the surface of the coated substrate. These spikes can result in short circuits in the completed optoelectronic device and hence reduce overall efficiency.
In PV devices, it is important the maximum amount of incident light enters into the cell in order to improve the efficiency of the cell (especially true at low angles of incidence), and one method of increasing the amount of light which can enter into photovoltaic cells is by ensuring that the light scattering (haze) of light, in particular light at longer wavelengths, is relatively high by using a relatively rough conductive coating.
However, with relatively rough surfaces, there is an increased likelihood of spikes (which can cause shunts) on the surface which result in the danger of short circuiting of the optoelectronic device.
There have been solutions proposed to this problem.
For example in Glass World Wide (30) 2010, pages 75 to 77, it is proposed to adjust the deposition method for deposition of conductive metal oxides in order to partially address the shunt problem.
In U.S. Pat. No. 6,225,640 a method of detecting and removing a shunt from a photoelectric semi-conductive device is disclosed using techniques including a dental probe, a laser or high speed grinder.
WO-2007/095322 discloses a chemical-mechanical polishing (CMP) composition and method for polishing an indium tin oxide (ITO) surface. The technique disclosed significantly smoothes the surface (changing the Ra) which is not advantageous in certain products (for example PV cells of certain sorts). The polishing technique disclosed in WO-2007/095322 is again relatively vigorous.
In Phys. Stat. Sol. (5) (2008) pages 3401 to 3404 (Lee, Woo-Sung) a CMP fabrication process is disclosed for organic light emitting diodes. The ITO coatings are deposited by RF magnetron sputtering. The CMP process is relatively vigorous using a relatively high polisher pressure and pad polishers.